0821 Nighttime Average and Dipping Blood Pressure Can Differ Based on the Temporal Distribution of Ambulatory Measurements at Nighttime

Abstract

Abstract Introduction Ambulatory blood pressure (BP) monitoring is recommended in preference to office BP as it enables BP assessments across the night and quantification of the degree of nocturnal BP dipping (dipping” = nighttime/daytime BP of < 0.9; non-dipping = ≥0.9). Both nighttime BP and dipping% are independent predictors of adverse cardiovascular events. Standard guidelines recommend at least ≥20/7 daytime/nighttime measurements for reliable ambulatory BP monitoring, but newer reports suggest ≥8/4 daytime/nighttime measurements are sufficient. Considering BP oscillates across the night, the temporal distribution of measurements across the night may impact nighttime BP and dipping%. To test whether this new recommendation holds for extreme examples of temporal distribution, we compared average nighttime BP and dipping% when using BP measurements only in the first (1st-half) vs. only in the second half (2nd-half) of the night. Methods Seventeen females and twenty-six males (50±10 years [mean±SD]) without cardiovascular disease or severe sleep disorders wore an ambulatory BP monitor for 24 hours, programmed to measure BP every 20 minutes when awake and every 30 minutes during a self-selected 8-hour time-in-bed for nighttime. We compared the nighttime BP averages and the calculated dipping% when using the first four measurements from the 1st-half of the nighttime, from the 2nd-half of the nighttime, and all measurements during the nighttime (All nighttime, AN). Repeated measures ANOVA was conducted with significance set as p< 0.05. Results Systolic BP was higher using 1st-half than 2nd-half but similar to AN (111±9 vs.107±11 vs. 109±9 mmHg, p< 0.01), while systolic BP dipping% using 1st-half was lower than 2nd-half and AN (9.7±7.4 vs.13.0±7.6 vs. 11.4±6.7 %, p< 0.01, respectively). Diastolic BP and diastolic dipping% were similar among the 1st-half, 2nd-half, and AN segment (63±6 vs. 63±7 vs. 62±7 mmHg, p=0.19) and (17.2±7.6 vs. 17.2±8.8 vs. 18.4±8.8 %, p=0.16), respectively. Conclusion In adults without cardiovascular disease or severe sleep disorders, nighttime BP and dipping% may depend upon when BP measurements are taken. The minimum threshold of 4 measurements for a reliable nighttime BP readout should be used cautiously. Support (if any) NIH F32-HL131308, R01HL163232, R01HL125893, R35HL155681, Medical Research Foundation, and OHSU OFDIR fellowship.